The stereochemistry of several steps in valine and leucine catabolism in mammals and microorganisms will be determined. In particular, the stereochemistry of the dehydrogenation of isobutyryl CoA to methacrylyl CoA, and the dehydrogenation of isovaleryl CoA to beta-methylcrotonyl CoA will be determined. The stereochemistry of the hydration of beta-methylcrotonyl CoA will be determined. The stereochemistry of the hydroxylation of valine to beta-hydroxyvaline will be determined.